> ## Documentation Index
> Fetch the complete documentation index at: https://ctrlrun.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Action and hash

> An action is a named operation with canonical arguments, a resource, a principal and an environment.

An action is one proposed operation, normalized: a name such as `stripe.refund`, its arguments
in canonical form, the resource it touches, the principal proposing it, and the environment it
runs in. The action hash is the SHA-256 of that canonical form, and it is the value every
approval is bound to.

## What the canonical form is

Two calls that mean the same thing must hash the same, and two that differ in anything a human
would care about must hash differently. So the form is fixed:

* keys sorted, recursively;
* no insignificant whitespace, `separators=(",", ":")`;
* UTF-8, `ensure_ascii=False`;
* argument values are `str`, `int`, `bool`, `None`, or nested containers of those;
* **`float` is rejected at any depth.** `0.1` and `0.10` are the same money and different
  bytes, so amounts are integer minor units: `200000` is €2,000.00.

The `action_id`, a fresh identifier per proposal, is excluded from the hash on purpose. Two
proposals of the same action from the same principal hash the same, which is what lets an
approval granted against the first pass of a LangGraph node match the second.

```python runnable theme={null}
from ctrlrun import Action, Principal, action_hash

who = Principal(agent="refund-agent")
first = Action(name="stripe.refund", arguments={"payment_id": "txn_2", "amount": 200000}, principal=who)
same = Action(name="stripe.refund", arguments={"amount": 200000, "payment_id": "txn_2"}, principal=who)
more = Action(name="stripe.refund", arguments={"payment_id": "txn_2", "amount": 500000}, principal=who)

assert action_hash(first) == action_hash(same)
assert action_hash(first) != action_hash(more)
print(action_hash(first)[:16], "==", action_hash(same)[:16])
```

## The guarantee it supports

Approval binding. A human approves a hash, and only the action with that hash can consume the
approval. Change the amount, the payment, the principal or the environment and the hash moves.

## What it does not do

The hash does not identify a *consequence*. Two different actions can cause the same effect,
and one action can be proposed twice; the effect key, not the hash, is what stops a duplicate.
The hash also says nothing about whether the arguments are sensible; the policy does.

## Next

* [Approval binding](/concepts/approval-binding): what the hash is for.
* [Effect keys](/concepts/effect-keys): the other identity, for the consequence.
* [Why](/why) · [Get started](/get-started/quickstart).


## Related topics

- [action_hash](/reference/api/action_hash.md)
- [Action](/reference/api/Action.md)
- [Receipt and event schemas](/reference/receipt-and-event-schemas.md)
- [Claims](/CLAIMS.md)
- [Principal](/reference/api/Principal.md)